Binoculars for Alaska

﻿Porro Prism﻿

﻿Roof Prism﻿

﻿Exit Pupil﻿

BINOCULARSBinoculars are not scary. They are all defined by the same specs. There are only two important numbers. First number refers to magnification power. Second number is the diameter of the objective lens (the one you don’t look through)--the big one that captures the light). Example: 10x50. 10X is ten times closer than when viewed with naked eye. The 50 allows more light than a 20. Both are measured in millimeters.Here are a few helpful definitions:﻿Field of view﻿--looking through binoculars, the widest dimension you can see is field of view.Exit pupil--hold your binoculars a foot or so away and look through the eyepiece—it actually looks like a pupil. The diameter of the exit pupil determines how much light is transmitted to your eye. This does not matter much on bright days, but in low light it makes a difference.Eye relief--distance between your eye and the eyepiece (ocular lens). If the viewer’s eye is outside this distance, a reduced field of view will be experienced. Many eye cups are used for eyeglasses and non-eyeglasses and ca be adjusted in or out.﻿Nitrogen purged--a process that removes the air from the binoculars and is filled with nitrogen, keeping moisture from being trapped and condensation from developing within the chambers. If a binocular is nitrogen purged, it is completely sealed from moisture.Coating of lenses--the coating is an anti-reflective coating. Multi-coating prevents light loss and offers better image contrast. Objective and ocular lenses are coated, but the best is fully multi-coated. If multi-coated, even the prism and eye pieces have been coated.Prism types--Roof prism and Porro prism. Binoculars with roof prisms have a straight tube. The front objective lens is in line with the ocular lens, making it more compact. With porro prisms, the objective lens is not in line with the ocular lens.﻿Porro prism﻿has only four reflectors, allowing a better viewing.﻿ Roof prisms ﻿have six reflectors, but with the improvement with the reflectors and the compact body are the more popular today.﻿﻿﻿﻿A good site to visit for information, price and brands is binoculars.com. View their binocular 101 videos.﻿﻿﻿﻿